1. Field of the Invention
The present invention relates to a sheet post-processing device that binds paper sheets carried out from an image forming device such as a printer or a copier and folds the bound paper sheets along a predetermined folding line and, more particularly, to a paper-made staple that binds the paper sheets.
2. Description of the Related Art
A sheet post-processing device that aligns paper sheets carried out from an image forming device and staples the paper sheets or folds the paper sheets in a booklet form is widely known. Such a sheet post-processing device is provided with a plurality of sheet accumulation means for sheet post-processing. For example, in a processing tray as a first sheet accumulation means, the paper sheets are accumulated in a bundle and are then stapled and, in a stacker section as a second sheet accumulation means, the paper sheets accumulated in a bundle are subjected to saddle stitching and then folded in a booklet form. In recent years, a binding processor that binds a paper sheet bundle without use of a metallic binding needle (metallic staple) in the sheet bundle binding processing and a sheet post-processing device are being provided.
For example, Jpn. Pat. Appln. Laid-Open Publication No. 2011-201698 discloses a device that performs bookbinding without use of a metallic binding staple so as to enhance recyclability and safety of the bound recording material bundle. In this device, a folding blade and a folding roller apply folding to a paper sheet bundle stacked on a stacker for stacking a plurality of paper sheets in order. A binding mechanism section binds the paper sheet bundle, without use of the metallic staple, in a position at a predetermined interval from a folding position where the paper sheet bundle is subjected to folding by the folding blade and the folding roller.
In the binding processing, the binding mechanism section causes deformation in a thickness direction of the paper sheet bundle that has been subjected to folding by the folding blade and the folding roller so as to bind the paper sheet bundle. More specifically, upper and lower concavo-convex teeth crimping teeth are meshed with each other to cause local deformation in the thickness direction of the paper sheet bundle to make the paper sheets to be engaged with each other.
Besides, there is known a cutter mechanism as a different type of binding mechanism from the binding mechanism using the crimping teeth. The cutter mechanism makes a cut in the paper sheet bundle for deformation of the cut part so as to bind the paper sheet bundle. More specifically, the cutter mechanism binds the paper sheet bundle by means of a U-shaped blade for making a U-shaped cut in the paper sheet bundle, a slit blade for forming a slit-like cut of a length corresponding to a width of the U-shaped blade, and a pushing-in means for pushing the U-shaped cut formed by the U-shaped blade in the slit-like cut.
In either of the above two mechanisms, a portion to which the binding mechanism applies binding is set so as to be separated by a predetermined interval from the folding position of the paper sheet bundle (refer to FIGS. 7 and 11 of Jpn. Pat. Appln. Laid-Open Publication No. 2011-201698). In other words, the folding position and binding position are shifted from each other.
Jpn. Pat. Appln. Laid-Open Publication No. 2013-126904 discloses a device including a cut forming section that forms a cut bent in a convex shape on one side of a paper sheet bundle and a binding portion forming section that forms, inside a range surrounded by the convex-shaped cut, a binding portion for binding the paper sheet bundle, wherein a line connecting both end portions of the convex-shaped cut is set as a folding line along which the paper sheet bundle is folded in two.
To be more specific, the above configuration is realized by a press device. The press device is provided with a punch section and a die section and configured to apply punching to the paper sheet bundle by the punch section. The punch section has an engagement piece forming blade, a hole forming blade, and a cut forming blade (FIG. 5). The engagement piece forming blade makes a cut in the paper sheet blade to form an engagement piece in the paper sheet. The hole forming blade forms, in the paper sheet, a locking piece which is a hole through which the engagement piece is inserted. The cut forming blade forms a cut in the paper sheet. The cut forming blade is bent (curved) into a shape protruding to one side. Both end portions of the engagement piece forming blade and both end portions of the cut forming blade are positioned on the same straight line. The paper sheet bundle is conveyed such that the folding line of the sheet bundle coincides with the straight line. On the other hand, the die section has a first insertion hole into which the engagement piece forming blade is inserted, a second insertion hole into which the hole forming blade is inserted, and a third insertion hole into which the cut forming blade is inserted.
Thus, the both end portions of the engagement piece forming blade and both end portions of the cut forming blade are positioned on the same straight line, and the folding line is set on this straight line. That is, as in Jpn. Pat. Appln. Laid-Open Publication No. 2011-201698, the folding position and binding position are shifted from each other.
Japanese Patent No. 4,952,129 discloses a stapler device that uses a paper-made staple in place of a metallic staple in consideration of environment and safety. In this device, an operator manually inserts a paper sheet bundle into a binding processing port. More specifically, Japanese Patent No. 4,952,129 discloses a desk-top type stapler device. In this device, a paper-made staple at the top of a connected staple in which a plurality of substantially straight shaped paper-made staple are connected in parallel is cut off from the connected staple and shaped into a substantially U-form. Then, both leg portions of the paper-made staple are made to penetrate paper sheets to be bound, bent along the paper sheets to be bound, and then bonded to each other. With this configuration, it is possible to bind the paper sheets to be bound with an easily deformable paper-made staple.
All of the above disclosed inventions are devices that bind the paper sheet bundle at a middle portion thereof and have a configuration in which the folding position and binding position are shifted from each other. The invention disclosed in Japanese Patent No. 4,952,129 is a device that does not use a metallic staple but uses a paper-made staple to bind the paper sheet bundle.
When the binding processing and folding processing are performed without use of the metallic staple in the above sheet post-processing devices that align paper sheets carried out from an image forming device or the like and staples the paper sheets or folds the paper sheets in a booklet form, the following problems arise in terms of device configuration.
As disclosed in Jpn. Pat. Appln. Laid-Open Publications No. 2011-201698 and No. 2013-126904, a portion to which the binding mechanism applies binding is set so as to be separated by a predetermined interval from the folding position of the paper sheet bundle. In other words, a booklet is formed with the folding position and binding position shifted from each other. However, as compared with a configuration in which a stapler position (binding position) and folding position are set at substantially the same position, a page opening range differs between a page where the binding position is formed and a page where the binding position is not formed due to shifting of the binding position from the folding position.
Thus, unless a printing area is reduced for the page having the binding position, image missing may occur. Further, when the folding position is set at a half position of a length of the paper sheet, since the binding position is shifted from the folding position, the first half pages can be turned beyond the folding position, whereas the remaining half pages can be turned only to the binding position separated away from the folding position. Thus, unbalance is generated in the page opening range in the same booklet, causing a feeling of strangeness.
The binding mechanisms disclosed in Jpn. Pat. Appln. Laid-Open Publications No. 2011-201698 and No. 2013-126904 are each configured to bind the paper sheet bundle by deforming the paper sheets themselves. For example, upper and lower concavo-convex teeth crimping teeth are meshed with each other to cause the deformation in the thickness direction of the paper sheet bundle to make the paper sheets to be engaged with each other. However, it is necessary to mesh the upper and lower concavo-convex crimping teeth with a considerable crimping force in order to make the paper sheets to be engaged with each other. An insufficient crimping force results in insufficient binding, that is, only the crimping force cannot make the binding state staple. When the binding position is made to coincide with the folding position in the binding mechanism using this crimping mechanism, a deformation force due to curve of the paper sheets acts to affect binding performance.
Further, as another binding mechanism, there is known the mechanism including a cut forming section that forms a cut bent in a convex shape on one side of a paper sheet bundle and a binding portion forming section that forms, inside a range surrounded by the convex-shaped cut, a binding portion for binding the paper sheet bundle, wherein the convex-shaped cut is inserted into the binding portion for binding. In this case, a comparatively large cut is formed in the paper sheets themselves, so that damage is given to the paper sheets themselves, and outer appearance is affected.
Under such circumstances, the binding mechanism by the paper-made staple as disclosed in Japanese Patent No. 4,952,129 that binds the paper sheet bundle without use of the crimping mechanism or without forming large cut in the paper sheets can be considered effective. However, in this mechanism, the operator manually inserts an end edge of the paper sheet bundle into a binding processing port, and the configuration described above, in which the paper sheet bundle is folded at the half position of the paper sheet length and bound is not considered at all. As a matter of course, a configuration in which the binding position of the paper sheet bundle and folding position are set at substantially the same position is not described.
Under such circumstances, the present inventor examines a configuration in which the paper-made staple is used to bind the paper sheet bundle at the half position of the paper sheet length and seeks to provide a sheet post-processing device capable of demonstrating a comparatively large binding force, capable of allowing left and right pages to be opened evenly upon page turning, capable of using the paper-made staple in the same way as the metallic one, and capable of providing an environmental benefit, and an image forming device adopting the sheet post-processing device.